Fluorescence analysis of natural aquatic environments, such as including oceanic, estuarine, or fresh waters, can be based on measurements of water emission, such as in response to a laser, LED, Xenon flash tube, or other sources of fluorescence excitation. Fluorescence analysis can be used to retrieve information about the fluorescent constituents in a water body or sample. For example, in vivo fluorescence of chlorophyll-a (Chl-a) and accessory phycobiliprotein (PBP) pigments can be broadly used as an index of phytoplankton biomass, and can provide useful information for structural or photo-physiological characterization of mixed algal populations. A broadband chromophoric dissolved organic matter (CDOM) fluorescence emission can be used to assess CDOM abundance, or to assess qualitative characteristics of CDOM.
There can be significant spectral complexity of the actively stimulated emission of natural waters. This can be due to an overlap between water Raman (WR) scattering and the fluorescence bands of aquatic constituents. Most commercially available field fluorometers use spectrally broad excitation sources and relatively narrow band emission detection, and often do not provide adequate spectral resolution to ensure reliable assessment of fluorescent constituents in spectrally complex natural waters.
Spectral measurements of water emission can be performed, such as using a plurality of light excitation sources, wherein at least one excitation source can have a wavelength that is different from other sources. Fluorescence and absorbance characteristics, such as over a plurality of wavelengths, can be detected. Hull et al., in U.S. Pat. No. 7,209,223, entitled OPTICAL DEVICE FOR MEASURING OPTICAL PROPERTIES OF A SAMPLE AND METHOD RELATING THERETO, refers to detecting a continuous, broadband spectrum of emission wavelengths, and a signal interpretation system to interpret a continuous fluorescence emission spectrum. Kolber et al., in U.S. Pat. No. 6,121,053, entitled MULTIPLE PROTOCOL FLUOROMETER AND METHOD, refers to measuring spectrally-resolved variable fluorescence components, among other functional and optical characteristics of phytoplankton and other plants.
Temporally-resolved measurements of water emission can be performed, such as using a light source, a cut-off filter, and photo-detector. Schrieber et al., in U.S. Pat. No. 4,084,905, entitled APPARATUS FOR DETECTING AND MEASURING FLUORESCENCE EMISSION, refers to detecting and measuring a time course of fluorescence, including using an initial fluorescence yield to measure chlorophyll concentrations.